This invention is related to a co-pending application entitled "Stabilized Multiparameter Control Product", Ser. No. 501,358, filed June 6, 1983 by the inventor hereof. That application is fully incorporated herein by reference.
Isoenzymes, or isozymes, as they are alternatively referred to, are enzymes in multiple forms which are capable of performing the same general function but at different rates. They are sufficiently different in chemical composition so that they are generally separable electrophoretically. One such isoenzyme, lactate dehydrogenase (LDH) is found in five electrophoretically distinct fractions. Each of these electrophoretic species of LDH is a tetramer consisting of two polypeptide chain units, H and M, present in different proportion: H.sub.4, MH.sub.3, M.sub.2 H.sub.2, HM.sub.3, and M.sub.4. These five isoenzymes differ in catalytic activity (affinity for the substrate, pyruvate as measured by the Michaelis constant), amino acid composition, heat lability, and immunological responses. The two peptides H and M are coded by different genes. Thus the type of enzyme present is under genetic control and regulated by the conditions of the environment imposed upon the cell.
Similarly, creatinine kinase (CK) is another isoenzyme which contains subunits of either M's or B's and thus may be present as MM, BB, or MB. The MB form is clinically significant as an indicator of myocardial information, however, this form is unstable and tends to disassociate to reform the MM or BB types. It is an object to stabilize a control reagent having the MB form.
The various proportions or combinations of isoenzymes present in the tissue may be related to the specific requirements of the cell in question and is thus affected by such factors as the extent of differentiation and development of the cell, as well as the level and type of metabolism occurring within the cell. Accordingly, the distribution between the various forms of isoenzymes provides diagnostically significant data. For instance, LDH exhibits significant control over cellular glycolosis. Specifically, MH.sub.3 and H.sub.4 isoenzyme types predominant in tissues with purely aerobic or respiratory metabolism. Accordingly, they may be used as diagnostic tools in determining the condition of muscles such as the heart--particularly with CK isoenzymes, the brain, liver and other organs in the case of alanine aminotransferase (ALT) or aspartase aminotransferase (AST). Yet another isoenzyme of significance is alkaline phosphatase gammaglutamyl transpeptidase.
With such attention being placed on the determination of isoenzyme levels, particularly important in the case of cardiac critical care patients, it is axiomatic that adequate controls must be available in order to ensure the proper operation of manual and automated methods designed to determine these levels. Heretofore, such controls as were available, have been typically unstable due to the highly unstable nature of the enzymes themselves.
It is an object of the present invention to provide control reagents having the necessary levels of isoenzymes present therein in a stabilized format.
It is another object of the present invention to provide methods whereby isoenzyme control reagents may be stabilized.